Method for producing homopolymers and copolymers of isobutene

ABSTRACT

In a process for the polymerization of isobutene or mixtures of isobutene with ethylenically unsaturated comonomers under the conditions of living cationic polymerization, the initiator system additionally comprises at least one nonpolymerizable, aprotic organosilicon compound having at least one Si—O bond.

The present invention relates to the preparation of homo- and copolymersof isobutene by cationic polymerization of isobutene or mixtures ofisobutene with ethylenically unsaturated comonomers which copolymerizewith isobutene under the conditions of a cationic polymerization.

Polyisobutene and its copolymers are used in various ways, for examplefor the preparation of fuel and lubricant additives, as elastomers, asadhesives or adhesive raw materials, as a base component of sealingcompounds and sealants, in coating systems, in particular those having awater vapor barrier effect, and in chewing gum materials. Blockcopolymers of isobutene with vinylaromatic monomers are distinguished,for example, by their elastomer properties and their high tightnessagainst permeation by gases.

The cationic polymerization of isobutene is frequently carried out byboron trifluoride catalysis, in particular by polymerization ofisobutene in the presence of boron trifluoride complex catalysts.Processes for this purpose are comprehensively described in the priorart (cf. for example DE-A 27 02 604, EP-A 145 235, EP-A 481 297, EP-A671 419, EP-A 628 575, EP-A 807 641 and WO 99/31151).

Kennedy et al. describe homo- and copolymerization of isobutene underthe conditions of a living cationic polymerization (cf. J. P. Kennedy etal. in U.S. Pat. Nos. 4,946,899, 4,327,201, 5,169,914, EP-A 206 756 andEP-A 265 053, and comprehensively in J. P. Kennedy, B. Ivan, DesignedPolymers by Carbocationic Macromolecular Engineering, Oxford UniversityPress, New York 1991). The initiator system used for the cationicpolymerization comprises, as a rule, at least one Lewis acid/metalhalide as catalyst and at least one organic compound which forms acarbocation or a cationic complex with the Lewis acid under the reactionconditions. Although the living cationic polymerization leads topolymers having high molecular uniformity and moreover, in contrast toboron trifluoride complex catalysis, also permits the controlledpreparation of block copolymers and of terminally functionalizedpolymers, it has to date been only of academic importance. This ispresumably due to the difficulty of controling it and its highrequirement with respect to the purity of the reagents used.

It has been reported variously that the reactivity of the initiatorsystems used for the living cationic polymerization can be controlled byadding donors. These are aprotic compounds having a nucleophilic, freeelectron pair. Examples of such donors are amides, such asN,N-dimethylacetamide and pyridine compounds. However, the use of suchdonors frequently results in poorly soluble precipitates on the reactorwalls, which adversely affect the quality of the polymerization product.The Applicant presumes that these deposits are due to the formation ofpoorly soluble adducts of donor compound and Lewis acid. Theinhomogeneities produced here lead in particular to a deterioration inthe molecular uniformity. Moreover, particularly in the case ofcontinuous processes, there is the danger that the deposits will lead toblockages, which may prevent control of the polymerization and, in anextreme case, may lead to the destruction of the plant.

It is an object of the present invention to provide a process for thepolymerization of isobutene and isobutene-containing monomer mixtureswhich leads to products having high molecular uniformity. Moreover, theprocess should not lead to deposits on the reactor walls to anysignificant extent, if at all, so that a continuous reaction procedureis possible.

We have found that this object is achieved, surprisingly, by apolymerization process of isobutene or mixtures of isobutene withethylenically unsaturated comonomers under the conditions of a livingcationic polymerization, in which the initiator system additionallycomprises at least one nonpolymerizable, aprotic organosilicon compoundhaving at least Si—O bond. It is presumed that the organosiliconcompound acts as a donor.

The present invention accordingly relates to a process for thepreparation of homo- and copolymers of isobutene by cationicpolymerization of isobutene or mixtures of isobutene with ethylenicallyunsaturated comonomers in the presence of an initiator systemcomprising:

-   i) a Lewis acid selected from covalent (semi)metal-halogen compounds-   ii) at least one aprotic organic compound I having at least one    functional group FG which, under polymerization conditions, forms a    carbocation or a cationic complex with the Lewis acid,    in an organic solvent which is inert to the Lewis acid, wherein the    initiator system additionally-   iii) comprises at least one nonpolymerizable, aprotic organosilicon    compound II having at least one Si—O bond.

In the novel process, the polymerization of the isobutene is initiatedby the initiator system comprising at least one Lewis acid, at least oneorganic compound I and at least one donor compound II which is anorganosilicon compound having at least one Si—O bond. It is assumed thatthe Lewis acid forms, with compound I, a carbocation or at least acationic complex which interacts with the olefinically unsaturateddouble bond of the isobutene or of the comonomer and generates apositive (partial) charge in the monomer, for example on the tertiarycarbon atom of the isobutene. This in turn interacts with a furtherisobutene molecule or a further monomer with continuation of thepolymerization reaction. Suitable compounds I are therefore all thosecompounds which are known to form a carbocation or at least a cationiccomplex with the abovementioned Lewis acids. It is assumed that thecomplex formed by compound I and the Lewis acid is stabilized by thedonor compound II or at least modified with regard to its reactivity.

The terms carbocation and cationic complex are not strictly separatedfrom one another but include all intermediate stages ofsolvent-separated ions, solvent-separated ion pairs, contact pairs andstrongly polarized complexes having a positive partial charge on acarbon atom of compound I.

Suitable compounds of the formula I are in principle all organiccompounds which have at least one nucleophilic displaceable leavinggroup X and which can stabilize a positive charge or partial charge onthe carbon atom which carries the leaving group X. These are known toinclude compounds which have at least one leaving group X which isbonded to a secondary or tertiary aliphatic carbon atom or to an allylicor benzylic carbon atom. Suitable leaving groups are in particularhalogen, C₁–C₆-alkoxy and C₁–C₆-acyloxy.

Here, halogen is in particular chlorine, bromine or iodine, especiallychlorine. C₁–C₆-Alkoxy may be either linear or branched and is, forexample, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy,n-pentyloxy or n-hexyloxy. C₁–C₆-Alkylcarbonyloxy is, for example,acetoxy, propionyloxy, n-butyroxy or isobutyroxy.

Preferred such compounds of the formula I are those in which thefunctional group is of the formula FG

in which

-   X is selected from halogen, C₁–C₆-alkoxy and C₁–C₆-acyloxy,-   R¹ is hydrogen or methyl and-   R² is methyl or, with R¹ or the moiety to which the functional group    FG is bonded, forms a C₅- or C₆-cycloalkyl ring, and R² may    furthermore be hydrogen if the functional group FG is bonded to an    aromatic or olefinically unsaturated carbon atom.

The compounds of the formula I preferably have one, two, three or four,in particular one or two, functional groups FG. X in the formula (FG) ispreferably a halogen atom, in particular chlorine.

Preferred compounds I are, for example, of the formulae I-A to I-D:

in which X has the abovementioned meanings,

-   n is 0, 1, 2, 3, 4 or 5,-   R³, R⁴ und R¹⁰, independently of one another, are each hydrogen or    methyl,-   R⁵, R⁶ and R⁷, independently of one another are each hydrogen,    C₁–C₄-alkyl or a group CR³R⁴-X, where R³, R⁴ and X have the    abovementioned meanings, and-   R⁸ is hydrogen, methyl or a group X and-   R⁹ and R⁹′ are each hydrogen or a group X.

In the formulae I-A to I-D, R³ and R⁴ are preferably both methyl. In theformula I-A, R⁶ is, for example, a group CR³R⁴-X which is arranged parato the CR³R⁴X group if R⁵ is hydrogen. It may also be in themeta-position if R⁵ is C₁–C₄-alkyl or a CR³R⁴-X group. Preferredcompounds I-A are, for example, 2-chloro-2-phenylpropane (cumylchloride) and 1,4-bis(2-chloroprop-2-yl)benzene (para-dicumyldichloride).

In formula I-B, R⁷ is preferably a CR³R⁴-X group or hydrogen. Examplesof compounds of formula I-B are allyl chloride, methallyl chloride,2-chloro-2-methylbut-2-ene and 2,5-dichloro-2,5-dimethylhex-3-ene.

In the compounds I-C, R³ is preferably methyl. R² is preferably likewisemethyl. R⁹ is preferably a group X, and in particular is halogen,particularly if R¹⁰ is methyl. Examples of compounds of the formula I-Care 1,8-dichloro-4-p-menthane (limonene dihydrochloride),1,8-dibromo-4-p-menthane (limonene dihydrobromide),1-(1-chloroethyl-3-chlorocyclohexane,1-(1-chloroethyl-4-chlorocyclohexane,1-(1-bromoethyl)-3-bromocyclohexane and1-(1-bromethyl)-4-bromocyclohexane.

Among the compounds of the formula I-D, those in which R⁸ is methyl arepreferred. Preferred compounds of the formula I-D are those in which R⁸is a group X, and in particular a halogen atom, if n is >0.

With regard to the use of the polyisobutenes prepared by the novelprocess as fuel or lubricant additives, preferred compounds I are thecompounds of the formula I-D, and among these in particular those inwhich X is halogen. In the formula I-D, n is preferably 1, 2, 3 or 4, inparticular 1 or 2, or is 0 when R⁸ is methyl. For many other purposes,in particular for the preparation of medium and relatively highmolecular weight polymers, for example having molecular weights above2000, in particular above 3000, Dalton, the compounds I-A are preferred.

As a rule, the compound I is used in the novel process in an amount ofat least 10⁻⁶ mol per mol of isobutene or per mol of polymerizablemonomers, in order to provide a sufficient concentration of initiatorcomplexes. As a rule, the amount of the compounds I will not exceed 1mol per mol of monomers to be polymerized (or isobutene). This and thedata given below regarding amounts of the compound I are always based onthe number of functional groups (FG) in the compound I, unless statedtherwise. Preferably, the compounds of the formula I are used in anamount of from 10⁻⁵ to 10⁻¹, in particular from 10⁻⁴ to 5×10⁻², mol,based on the functional groups (FG) of the compound I, per mol ofisobutene or polymerizable monomers. Here, it should be noted that theachieved molecular weight of the polyisobutene prepared by the novelprocess is dependent on the amount of compound I in such a way that themolecular weight of the polyisobutene decreases with increasingconcentration of compound I.

Suitable Lewis acids are in principle covalent metal halides andsemimetal halides, which as a rule have a missing electron pair. Suchcompounds are known to a person skilled in the art, for example fromKennedy et al., loc. cit., and as a rule are selected from covalentmetal-halogen compounds of titanium, of tin, of aluminum, of vanadium orof iron, and the halides of boron. The chlorides are preferred and, inthe case of aluminum, also the monoalkylaluminum chlorides and thedialkylaluminum chlorides. Examples of preferred Lewis acids aretitanium(IV) chloride, boron trichloride, tin(IV) chloride, aluminumtrichloride, vanadium(V) chloride, iron(III) chloride, C₁–C₆-alkyl-AlCl₂and (C₁–C₆-alykyl)₂AlCl. Particularly preferred Lewis acids aretitanium(IV) chloride and boron trichloride.

The Lewis acid is of course used in the novel process in an amount whichis sufficient for formation of the initiator complex. This is as a ruleensured even at low concentrations of Lewis acid in the reaction medium.Preferably, the molar ratio of Lewis acid to compound I is from 20:1 to1:20, in particular from 10:1 to 1:10. The concentration of the Lewisacid in the reaction medium is as a rule from 10⁻³ to 1, preferably from5×10⁻³ to 0.3, in particular from 0.01 to 0.2, mol/l.

The nonpolymerizable, aprotic organosilicon compounds II are as a rulethose compounds which have at least one organic radical bonded via anoxygen atom and having as a rule 1 to 20 carbon atoms. Examples of suchradicals are alkoxy, cycloalkoxy, aryloxyl, arylalkoxy and acyloxy(alkylcarbonyloxy).

Alkyl is understood as meaning a linear or branched saturatedhydrocarbon radical of, as a rule, 1 to 20, preferably 1 to 10, carbonatoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,tert-butyl, 2-butyl, n-pentyl, 2-methylbut-1-yl, 2-methylpent-1-yl,2-ethylbut-1-yl, n-hexyl, 2-methylhex-1-yl, 2-ethylhex-1-yl, n-heptyl,n-octyl, isooctyl, n-decyl and comparable radicals.

Aryl is an aromatic hydrocarbon radical of, as a rule, 6 to 20 carbonatoms, such as phenyl, naphthyl and comparable groups which may have oneor more C₁–C₁₀-alkyl groups as substituents, e.g. tolyl,isopropylphenyl, xylyl or tert-butylphenyl.

Here, cycloalkyl is as a rule a 5-, 6- or 7-membered, saturatedcarbocyclic structure which may have one or more C₁–C₁₀-alkyl groups assubstituents.

Arylalkyl is an aryl radical of, as a rule, 1 to 10, preferably 1 to 4,carbon atoms, which is substituted by an aryl radical as defined above,e.g. is benzyl or 2-phenylethyl.

Alkyloxy is alkyl bonded via an oxygen atom. Accordingly, aryloxy,cycloalkoxy and arylalkoxy are aryl, cycloalkyl and arylalkyl,respectively, bonded via an oxygen atom.

Acyloxy is an alkylcarbonyl radical which is bonded via oxygen andpreferably has 1 to 6 carbon atoms in the alkyl moiety, for example isacetoxy, propionyloxy, butyroxy, etc.

The organosilicon compounds II may have one or more, e.g. 2 or 3,silicon atoms with at least one organic radical bonded via oxygen.Preferred organosilicon compounds II are those which have one, two orthree, in particular 2 or 3, radicals bonded via oxygen per siliconatom.

Preferred organosilicon compounds are those which are of the formula II:R^(a) _(n)Si(OR^(b))_(4-n)where n is 1, 2 or 3,

-   R^(a) may be identical or different and, independently of one    another, are each C₁–C₂₀-alkyl, C₅–C₇-cycloalkyl, aryl or    aryl-C₁–C₄-alkyl, it being possible for the three last-mentioned    radicals also to have one or more C₁–C₁₀-alkyl groups as    substituents, and-   R^(b) are identical or different and are each C₁–C₂₀-alkyl or, where    n is 1 or 2, two different radicals Rb together may also form a 2-    or 3-membered alkylene unit.

In formula II, n is preferably 1 or 2. R^(a) is preferably C₁–C₈-alkyland in particular alkyl which is branched or is bonded via a secondarycarbon atom, such as isopropyl, isobutyl, 2-butyl or a 5-, 6- or7-membered cycloalkyl group. R^(b) is preferably C₁–C₄-alkyl.

Examples of such preferred compounds are dimethoxydiisopropylsilane,dimethoxyisobutylisopropylsilane, dimethoxydiisobutylsilane,dimethoxydicyclopentylsilane, dimethoxyisobutyl-2-butylsilane,diethoxyisobutylisopropylsilane, triethoxytoluylsilane andtriethoxybenzylsilane.

In the novel process, the organosilicon compound II is used in an amountsuch that the molar ratio of silicon atoms in the organosilicon compoundII to the metal atoms or the semimetal atoms in the Lewis acid is from0.05:1 to 50:1, preferably from 0.1:1 to 10:1, particularly preferablyfrom 0.1:1 to 2:1. Very particularly preferably the organosiliconcompound II is used in a substoichiometric amount (calculated as theratio of the silicon atoms to the (semi)metal atoms).

Both isobutene as such and monomer mixtures of isobutene witholefinically unsaturated monomers which are known to be copolymerizablewith isobutene under cationic polymerization conditions can be reactedby the novel process. The novel process is moreover suitable for theblock copolymerization of isobutene with ethylenically unsaturatedcomonomers polymerizable under cationic polymerization conditions. Ifmonomer mixtures of isobutene are to be polymerized with suitablecomonomers, the monomer mixture preferably contains more than 80, inparticular more than 90, particularly preferably more than 95, % byweight of isobutene and less than 20, preferably less than 10, inparticular less than 5, % by weight of comonomers.

Suitable copolymerizable monomers are vinylaromatics, such as styreneand a-methylstyrene, C₁–C₄-alkylstyrenes, such as 2-, 3- and4-methylstyrene, and 4-tert-butylstyrene, isoolefins of 5 to 10 carbonatoms, such as 2-methylbut-1-ene, 2-methylpent-1-ene, 2-methylhex-1-ene,2-ethylpent-1-ene, 2-ethylhex-1-ene and 2-propylhept-1-ene. Suitablecomonomers are furthermore olefins which have a silyl group, such as1-trimethoxysilylethene, 1-(trimethoxysilyl)propene,1-(trimethoxysilyl)-2-methylprop-2-ene,1-[tri(methoxyethoxy)silyl]ethene, 1-[tri(methoxyethoxy)silyl]propeneand 1-[tri(methoxyethoxy)silyl]-methylprop-2-ene.

Preferred embodiments of the novel process relate to thehomopolymerization of isobutene or isobutene-containing startingaterials and the block copolymerization of isobutene with vinylaromaticmonomers. Here, the isobutene starting materials contain, as a rule,less than 5% by weight, based on the total amount of theisobutene-containing starting material, of copolymerizable monomers. Forthe block copolymerization, this is true in an analogous manner also forthe vinylaromatic monomers.

Suitable isobutene starting materials for the novel process are bothisobutene itself and isobutene-containing C₄-hydrocarbon streams, forexample refined C₄ fractions, C₄-cuts from isobutene dehydrogenation,C₄-cuts from steam crackers and FCC crackers (FCC: Fluid CatalysedCracking), provided that they have been substantially freed from1,3-butadiene contained therein. C₄-Hydrocarbon streams suitableaccording to the invention contain, as a rule, less than 500, preferablyless than 200, ppm of butadiene. When C₄-cuts are used as startingmaterial, the hydrocarbons other than isobutene play the role of aninert solvent.

As a rule, the novel process is carried out at below 0° C., for examplefrom 0 to −140° C., preferably from −30 to −120° C., particularlypreferably from −40 to −110° C. The reaction pressure is of minorimportance and depends in a known manner on the apparatuses used andother reaction conditions.

Suitable solvents are all organic compounds which differ from thecompounds I and II and the polymerizable monomers, in particularisobutene, and which have no abstractable protons. Preferred solventsare acyclic alkanes of 2 to 8, preferably 3 to 6, carbon atoms, such asethane, isopropane, n-propane, n-butane and its isomers, n-pentane andits isomers, n-hexane and its isomers and n-pentane and its isomers,cycloalkanes of 5 to 8 carbon atoms, such as cyclopentane, cyclohexaneand cycloheptane, acyclic alkenes of, preferably, 2 to 8 carbon atoms,such as ethene, isopropene, n-propene, n-butene, n-pentene, n-hexene andn-heptene, cyclic olefins, such as cyclopentene, cyclohexene andcycloheptene, aromatic hydrocarbons, such as toluene, xylene,ethylbenzene or chlorobenzene, halogenated alkanes of 1 to 5 carbonatoms and 1, 2, 3, 4, 5 or 6 halogen atoms, selected from fluorine andin particular chlorine, such as methyl chloride, dichloromethane,trichloromethane, ethyl chloride, 1,2-dichloroethane and1,1,1-trichloroethane and chloroform.

It is not only the solvents as such that are suitable but also mixturesof these solvents. Mixtures are preferred particularly when the solventhas a melting point above the desired polymerization temperature.

Solvents and solvent mixtures which comprise at least one cyclic oralicyclic alkane and/or an α-olefin are particularly preferred.Particularly preferred among these are solvent mixtures which compriseat least one nonhalogenated hydrocarbon and at least one halogenatedhydrocarbon, preferably an aliphatic or cycloaliphatic alkane andchlorinated hydrocarbons. Of course, the chlorinated hydrocarbons do notinclude any compound in which chlorine atoms are present on secondary ortertiary carbon atoms.

The polymerization is of course carried out under substantially aprotic,in particular under anhydrous, reaction conditions. Aprotic or anhydrousreaction conditions are understood as meaning that the water content (orthe content of protic impurities) in the reaction mixture is less than50 ppm, in particular less than 5 ppm. As a rule, the starting materialsare therefore dried physically and/or by chemical measures before theyare used. For example, after conventional preliminary purification andpreliminary drying, the aliphatic or cycloaliphatic hydrocarbonspreferably used as solvents can be mixed with an organometalliccompound, for example an organolithium compound, for example anorganolithium, organomagnesium or organoaluminum compound, in an amountsufficient for removing traces of water from the solvent. The solventtreated in this manner can be condensed directly into the reactionvessel. It is also possible to proceed in a similar manner with theα-olefins, the aromatic hydrocarbons and the monomers to be polymerized,in particular the isobutene.

The preliminary purification or preliminary drying of the solvents andof the isobutene is effected in a conventional manner, preferably bytreatment with solid drying agents, such as molecular sieves or predriedoxides, such as calcium oxide or barium oxide. The starting materialsfor which treatment with metal alkyls is not suitable, for example thealkyl halides used as solvents and the compounds I and II, can be driedin an analogous manner.

The polymerization of the isobutene or of the isobutene-containingmonomer mixture takes place spontaneously on mixing of the initiatorsystem used according to the invention with the isobutene or with theisobutene-containing monomer mixture in the inert organic solvent at thedesired reaction temperature. Here, for example, it is possible toproceed in such a way that isobutene or the monomer mixture is initiallytaken in the inert solvent and cooled to the reaction temperature andthe initiator system then added. It is also possible to proceed in sucha way that the initiator system is initially taken in the solvent andthen the isobutene or the isobutene-containing monomer mixture is addedall at once or at the rate at which it is consumed. In addition, a partor the total amount of the isobutene or of the isobutene-containingmonomer mixture can be initially taken in the solvent and the initiatorsystem then added. The remaining amounts of isobutene orisobutene-containing monomer mixture are then added in the course of thereaction, for example at the rate at which it is consumed.

The initiator system is as a rule added by introducing the components ofthe initiator system separately. In the batchwise procedure, as a rule,the compound I and the compound II are first added, followed by theLewis acid. The time of addition of the initiator is then considered tobe the time when all components of the initiator system are present inthe reaction vessel. For example it is possible for first the solvent,then the compound I and the compound II and then a part of the totalamount of the isobutene or of the isobutene-containing starting materialto be additionally taken, the polymerization initiated by adding theLewis acid and then, if required, any remaining amounts of isobutene orisobutene-containing starting materials fed to the polymerization.However, it is also possible for first the solvent, then the Lewis acidand then a part or the total amount of the isobutene or of theisobutene-containing starting material to be initially taken and thenthe polymerization initiated by adding the compound I and the compoundII.

In addition to the batchwise procedure described here, thepolymerization can also be designed as a continuous process. Here, thestarting materials, i.e. the monomers to be polymerized, the solvent andthe initiator system, are fed continuously to the polymerizationreaction and the reaction product is removed continuously, so that moreor less steady-state polymerization conditions are established in thereactor. The components of the initiator system can be fed in eitherseparately or together, preferably diluted in the solvent. The isobuteneto be polymerized or the isobutene-containing monomer mixture can be fedin as such, diluted with a solvent or as an isobutene-containinghydrocarbon stream.

For example, the addition of the components of the isobutene systemdiluted in the solvent can be effected via multimaterial nozzles inorder to achieve thorough mixing of the components.

The removal of the heat of reaction in the batchwise as well as in thecontinuous reaction is effected in a conventional manner, for example bymeans of internally installed heat exchangers and/or by cooling of thewalls and/or by utilizing evaporative cooling. Here, the use of etheneand/or mixtures of ethene with other hydrocarbons and/orhalohydrocarbons as solvent has proven particularly useful since etheneis not only economical but also has a boiling point in the desiredpolymerization temperature range.

In principle, all reactors as usually used for cationic polymerizationof isobutene, for example cationic polymerization of isobutene withboron trifluoride-oxygen complexes, are suitable as reaction vessels forcarrying out the novel process. To this extent, reference is made hereto the relevant prior art. In the batchwise reaction procedure, thestirred kettles which are customary for this purpose and are preferablyequipped with evaporative cooling, suitable mixers, feeds, heatexchanger elements and blanketing apparatuses are suitable. Thecontinuous reaction procedure can be carried out in the reactionkettles, reaction cascades, tubular reactors, tube-bundle reactors, inparticular tubular and tube-bundle reactors arranged in a circle, whichare preferably equipped in the manner described above for reactionkettles.

In order to recover the isobutenes from the reaction mixture, the latteris deactivated after the polymerization in the manner customary forcationic polymerization reactions, preferably by adding a proticcompound, in particular by adding alcohols, such as methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol ortert-butanol, or mixtures thereof with water. Preferably, the substancesused for the deactivation are employed in a diluent, for example one ofthe solvents, in order to avoid an undesired increase in viscosity.Otherwise, here too reference may be made to the prior art cited at theoutset and relating to the polymerization of boron trifluoride withisobutene, whose working-up measures can be applied in an analogousmanner to the novel process.

In a further embodiment of the invention, the polymerization is stoppedby adding a trialkylallylsilane compound, for example by addingtrimethylallylsilane ((CH₃)₃Si—CH₂—CH═CH₂). Such compounds are usuallyused in amounts of from 0.3 to 3, preferably from 0.5 to 1.5, mol permol of functional groups FG. The use of the allylsilane leads tostoppage of the polymerization with introduction of a propenyl group atthe end of the polymer chain. For further details relating to thisreaction, reference is made at this point to EP-A 713 883.

Preferably, the composition used for the deactivation or the mixturethereof with an inert solvent is cooled to polymerization temperaturebefore the deactivation, in order to avoid undesired secondaryreactions.

The solvent is then removed in suitable units, such as rotary,falling-film or thin-film evaporators, or by means of flash evaporation(this is understood as meaning letting down the reaction solutiondownstream of a heat exchanger into pipelines or via a perforated plateor die plate). For removal of the solvent, reduced pressure ispreferably applied, for example from 0.1 to 800, in particular from 1 to100, mbar. Bottom temperatures of from 50° to 250° C., in particularfrom 150 to 220° C., are preferred.

For the preparation of block copolymers of isobutene and vinylaromaticmonomers, as a rule the first isobutene or a monomer mixturesubstantially comprising isobutene, in one of the abovementionedsolvents, is reacted in the presence of the novel initiator system at,preferably, below 0° C., in particular from −20 to −120° C.,particularly preferably from −50 to −110° C., until the desiredconversion of the isobutene is reached. The vinylaromatic monomers arethen added to produce the further polymer blocks. During or after theaddition of the vinylaromatic monomers, the reaction temperature can bemaintained or, depending on the reactivity of the vinylaromaticcompound, can be increased. The polymerization of the vinylaromaticmonomers is preferably carried out at above −50° C., for example from−50 to +50° C. As a rule, the polymerization of the isobutene iscontinued until a conversion of at least 80%, preferably at least 90%,before the vinylaromatic monomers are added. The addition of thevinylaromatic monomers is preferably effected before 99%, in particularbefore 98%, of the isobutene have reacted, since otherwise there is thedanger that some of the active terminal groups will be deactivated.

This ensures the initial formation of a polymer block which issubstantially composed of isobutene units and carries, at one end or,with the use of polyfunctionalized compounds I, at its ends, polymerblocks which are composed of vinylaromatic monomers, and which aresubstantially unsegmented, i.e. free of isobutene units. Such blockcopolymers are of interest in particular as sealing materials.

The novel process is moreover particularly suitable for the preprationof polyisobutenes, i.e. polymers which are composed of at least 80,preferably at least 90, % of isobutene in the form of polymerized units.Polyisobutenes having number average molecular weights (M_(n)) of from400 to 400000, preferably from 500 to 200000 particularly preferablyfrom 700 to 100000, Dalton, are obtainable by the novel process.Preferably, the process of the invention is suitable for the preparationof polyisobutenes having number average molecular weights above 2000, inparticular above 3000, Dalton. The molecular weight can be varied by aperson skilled in the art in a simple manner by varying theconcentration of compound I used, a high concentration of compound Ileading to polymers having a low molecular weight and a lowconcentration of compound I leading to polymers having higher molecularweights. The same also applies to the preparation of the vinylaromaticpolymer blocks in the block copolymers. In addition, the polymersobtained from the novel process have functional terminal groups, forexample halogen atoms or olefinically unsaturated double bonds, whichcan be used for further functionalization measures. This is of interestin particular for the preparation of fuel and lubricant additives, whichas a rule are composed of a hydrophobic hydrocarbon radical, for examplea polyisobutenyl group, and a hydrophilic moiety.

The polymers prepared by the novel process suprisingly have a narrowmolecular weight distribution. The dispersity D (quotient of the weightaverage molecular weight M_(w) divided by the number average molecularweight M_(n)) of the polymers prepared by the novel process ispreferably below 1.6, in particular below 1.4, particularly preferablyfrom 1.05 to 1.3.

All data on molecular weights relate to values determined by means ofgel permeation chromatography (GPC). The gel permeation chromatographywas carried out using THF as mobile phase and CS₂ as reference on twocolumns connected in series (1300 mm, d 7.8 mm), the first column beingpacked with Styragel HR5 (molecular weight range from 50000 to 4×10⁶)and the second column with Styragel HR3 (molecular weight range from 200to 30000) from Waters. The detection was effected by means of adifferential refractometer. The standards used for determining theisobutene block were commercial polyisobutene standards in the molarmass range from 224 to 1000000, from Polymer-Standards Service, Mainz,Germany. In the determination of the molecular weight of the blockcopolymers, a polystyrene calibration file and a UV detector wereadditionally used.

The examples which follow illustrate the invention without restrictingit.

I. Analysis

The determination of the molecular weight was carried out by means ofgel permeation chromatography (GPC) against polyisobutene standards inthe manner described above.

II. General Preparation Method for a Polymerization Process

Two 1 l dropping funnels with cooling apparatus were placed on a 2 lfour-necked flash having a stirrer and cooled with dry ice. Bothdropping funnels contained a bed of dry molecular sieve 3 Å over glasswool.

In one dropping funnel, 600 ml of a solvent mixture were dried for 20minutes at −78° C. The solvent was then metered into the reaction flask,which had been prethermostated at −70° C. Three moles of isobutene werecondensed into the other, cooled dropping funnel. The total amount ofisobutene was then introduced into the reaction flask in the course of25 minutes. While maintaining the temperature of −70° C., from 10 to 24mmol of donor compound II, from 15 to 35 mmol of compound I and then 40mmol of Lewis acid were then added in succession via a septum withvigorous stirring. After 3 hours, one mole of isopropanol was added at−70° C., the mixture was warmed up to room temperature and the reactionsolution was then washed with three times 200 ml of water. The reactionsolution was then evaporated down and dried at 200° C. under reducedpressure, finally at 2 mbar. In this way, from about 140 to 160 g ofpolymer were obtained. The amounts used are shown in table 1. Theproperties of the polymer are listed in table 2.

TABLE 1 Starting materials Donor II¹⁾ Compound I²⁾ Lewis Example [mmol][mmol] Acid Solvent³⁾ 1 A 15 CC 35 TiCl₄ CH₂Cl₂/Hexane 2:1 2 B 15 CC 15TiCl₄ CH₂Cl₂/Hexane 2:1 3 C 10 CC 35 TiCl₄ Toluene/CH₂Cl₂/ Hexane 1:1:14 D 24 CC 35 TiCl₄ CH₂Cl₂/Hexane 2:1 5 A 15 CC 35 BCl₃ CH₂Cl₂/Hexane 2:16 A 24 pDCC 15 TiCl₄ CH₂Cl₂/Hexane 2:1 7 A 15 pDCC 15 TiCl₄Toluene/CH₂Cl₂/ Hexane 1:1:1 V1 Pyridine 15 CC 35 TiCl₄ CH₂Cl₂/Hexane2:1 V2 Pyridine 24 pDCC 15 TiCl₄ Toluene/CH₂Cl₂/ Hexane 1:1:1 V3 — — CC35 TiCl₄ CH₂Cl₂/Hexane 2:1 ¹⁾A = Dicyclopentyldimethoxysilane B =Diisopropyldimethoxysilane C = Isopropylisobutyldimethoxysilane D =Toluyltriethoxysilane ²⁾CC = Cumyl chloride (2-chloro-2-phenylpropane)pDCC = p-Dicumyl dichloride (1,4-bis(2-chloroprop-2-yl)benzene) ³⁾Partsby volume

TABLE 2 Polymer properties Molecular weight M_(n) Dispersity Example[Dalton] [M_(w)/M_(n)] 1 5800 1.12 2 12300 1.18 3 4900 1.26 4 4700 1.305 3200 1.08 6 15300 1.17 7 12300 1.14 V1 5200 1.31 V2 12300 1.34 V3 40002.30

1. A process for the preparation of homo- and copolymers of isobutene bycationic polymerization of isobutene or mixtures of isobutene withethylenically unsaturated comonomers in the presence of an initiatorsystem comprising: i) a Lewis acid selected from covalent metal-halogencompounds or covalent semimetal-halogen compounds, ii) at least oneaprotic organic compound I having at least one functional group FG ofthe formula FG

where X is selected from halogen, C₁–C₆-alkoxy or C₁–C₆acyloxy, R¹ ishydrogen or methyl and R² is methyl, with R¹ or the moiety to which thefunctional group FG is bonded, forms a C₅- or C₆-cycloalkyl ring, or ishydrogen when the functional group FG is bonded to an aromatic orolefinically unsaturated carbon atom, which, under polymerizationconditions, forms a carbocation or cationic complex with the Lewis acid,wherein the organic compound I is selected from compounds of the formulaI-A, I-B, I-C, or I-D:

where X has the abovementioned meanings, n is 1, 2, 3, 4 or 5, R³, R⁴and R¹⁰, independently of one another, are each hydrogen or methyl, R⁵,R⁶ and R⁷, independently of one another, are each hydrogen, C₁–C₄-alkylor a group CR³R⁴X, where R³, R⁴ and X have the abovementioned meanings,and R⁸ is hydrogen, methyl or the group X and R⁹ and R^(9,) are eachhydrogen or the group X, in an organic solvent which is inert to theLewis acid, wherein the initiator system additionally comprises iii) atleast one nonpolymerizable, aprotic organosilicon compound II having atleast one Si—O bond.
 2. The process as claimed in claim 1, wherein theorganosilicon compound is of the formula II:R^(a) _(n)Si(OR^(b))_(4-n)  (II) where n is 1, 2 or 3, R^(a) may beidentical or different and, independently of one another, are eachC₁–C₂₀-alkyl, C₅–C₇-cycloalkyl, aryl or aryl-C₁–C₄-alkyl, whereoptionally the three last-mentioned radicals also have one or moreC₁–C₁₀-alkyl groups as substituents, and R^(b) are identical ordifferent and are each C₁–C₂₀-alkyl or, where n=1 or 2, two differentradicals R^(b) together may also form a 2- or 3-membered alkylene unit.3. The process as claimed in claim 1, wherein the Lewis acid is selectedfrom BF₃ TiCl₄, SnCl₄, BCl₃, FeCl₃, VCl₅, AlCl₃ or R^(c)—AlCl₂, whereR^(c) is C₁–C₆-alkyl.
 4. The process as claimed in claim 3, wherein theLewis acid is selected from TiCl₄ or BCl₃.
 5. The process as claimed inclaim 1, wherein the molar ratio of silicon atoms in the organosiliconcompound II to (semi)metal atoms in the Lewis acid is from 0.05:1 to50:1.
 6. The process as claimed in claim 1, wherein the compound I isused in an amount of from 10⁻⁴ to 10⁻¹ mol, based on the functionalgroups FG of the compound I, per mol of polymerizable monomer.
 7. Theprocess as claimed in claim 1, wherein the molar ratio of the Lewis acidto the functional group FG of compound I is from 20:1 to 1:50.
 8. Theprocess as claimed in claim 1, wherein the polymerization is carried outat below 0° C.
 9. The process as claimed in claim 1, wherein the solventis selected from aliphatic or cycloaliphatic hydrocarbons, aromatichydrocarbons or inert halohydrocarbons.
 10. The process as claimed inclaim 1, wherein isobutene is copolymerized with at least onevinylaromatic monomer.
 11. The process as claimed in claim 10, whereinfirst isobutene and then the vinylaromatic monomer is polymerized. 12.The process as claimed in claim 1, wherein the polymerization is stoppedby adding an aprotic compound.
 13. The process as claimed in claim 1,wherein the polymerization is stopped by adding a tri(alkyl)allylsilanecompound.
 14. The process as claimed in claim 1 which is a; and theliving cationic polymerization of isobutene or mixtures of isobutenewith ethylenically unsaturated comonomers, wherein compound II functionsas a donor.